Financings - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	12 Months Ended	0 Months Ended
	Jan. 12, 2011	Dec. 31, 2014	Oct. 29, 2013	Oct. 23, 2013	Jan. 31, 2012	Jan. 25, 2012	Jan. 20, 2012	Feb. 17, 2015	Feb. 09, 2015	Feb. 03, 2015
Class of Stock [Line Items]
Stock issued during period	3,636,926
Expected net proceeds from issuance of common stock		$ 94.6
J.P. Morgan Securities Inc.
Class of Stock [Line Items]
Stock issued during period			2,145,000	14,300,000	464,401	9,650,000
Issuance & sale of common stock in public offering price per share				$ 3.50			$ 5.20
Option granted, exercisable period				30 days			30 days
Option to purchase common stock				2,145,000			1,447,500
Sale of stock price per share				$ 3.29			$ 4.888
Net proceeds from issuance of common stock			53.9		49.2
Issuance & sale of common stock in public offering							9,650,000
J.P. Morgan Securities Inc. | Total
Class of Stock [Line Items]
Stock issued during period					10,114,401
J.P. Morgan Securities Inc. | Subsequent Event
Class of Stock [Line Items]
Stock issued during period								1,500,000	10,000,000	10,000,000
Issuance & sale of common stock in public offering price per share										$ 8.75
Option granted, exercisable period										30 days
Option to purchase common stock										1,500,000
Sale of stock price per share										$ 8.225
Expected net proceeds from issuance of common stock								$ 94.2